A national security spokesman for the Republican presidential hopeful Mitt Romney resigned yesterday, saying critics had questioned his conservatism because he is gay.

Richard Grenell, who is openly gay, joined Mr Romney's campaign late last month.

"My ability to speak clearly and forcefully on the issues has been greatly diminished by the hyper-partisan discussion of personal issues that sometimes comes from a presidential campaign," Mr Grenell said in a statement.

A series of critics on the right had suggested Mr Grenell's sexuality would present problems for the Romney campaign. Mr Romney has struggled to court the religious wing of the Republican Party as he sought the nomination, having previously changed his position on social issues such as abortion.

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